1. Field of the Invention
This invention pertains generally to sensing key motion in keyboard operated musical instruments, and more particularly to a method and apparatus for dynamically sensing the position of a hammer shank in a piano and determining velocity and duration characteristics of a played note for electronic recording.
2. Description of the Background Art
Accurate recording of musical expression from a keyboard operated musical instrument such as a piano has long been of interest to musicians, composers, and listeners. Early versions of recording devices punched holes in paper ribbons or rolls for reproduction of musical notes by a "player piano." Advances in electronic and optical technologies have led to the development of more sophisticated and accurate sensing and recording means for keyboard instruments.
The availability of inexpensive and increasingly powerful data processing devices has further propelled development of keyboard recording systems. Sensing and recording systems now exist which are interfaced with microprocessors, with electronically or optically generated key information being digitized and interpreted by software. A standardized communication format for such software has been developed in the music industry under the name Musical Instrument Digital Interface or "MIDI."
Several devices, systems, and methods employing electronic or optical sensors on keyboard instruments are known. For example, U.S. Pat. No. 3,617,627 discloses a code converter suitable for use with a keyboard wherein a plurality of code bars corresponding to keys are mounted above a plurality of light channels. Depression of the code bars blocks the light from the light channels from reaching photocells.
U.S. Pat. No. 4,073,511 discloses a teaching device for attachment to an organ in which an aperture-containing record sheet is moved between a light source and fiber optic connectors. The fiber optic ends project light onto keys in accordance with the apertures recorded in the moving sheet.
U.S. Pat. No. 4,362,934 discloses a velocity sensing device using opto-electronic switches in which movement of keys on a musical synthesizer keyboard actuate flags. The flags block or expose light to detectors according to the position of the keys.
U.S. Pat. No. 4,468,999 discloses a programmable synthesizer having a keyboard which develops an expression signal representing pressure on the keys by detecting the change in path length of an infrared light signal.
U.S. Pat. No. 4,736,662 discloses an optical sensor for sensing displacement speed or displacement of a moveable element in a musical instrument, wherein light emitted from a source is guided via optical fiber to a detector. Movement of elements of the musical instrument actuate shutters which permit or prevent transmission of the emitted light to the detectors.
U.S. Pat. No. 4,674,069 discloses a system for collecting and processing data relating to moving bodies in which a frequency modulated ultrasonic wave is transmitted towards a moving body and the wave reflected therefrom is received by a detector and frequency demodulated. A signal representing the moving body is obtained using the frequency variation of the transmitted and received waves.
U.S. Pat. No. 4,790,230 discloses a low profile keyboard device and system for recording and scoring music comprising modular recording devices which are attached adjacent the keys of a keyboard. Key expression data is obtained by reflective couplers on the modular devices which reflect light off the keys. The expression data is then processed for scoring and recording.
U.S. Pat. No. 5,099,738 discloses a MIDI musical translator having a plurality of force sensitive transducers in a keyboard arrangement. The keyboard is electronically scanned, and the information relating to the velocity of the key depression is recorded and converted to standardized MIDI information to be used for subsequent musical tone generation.
U.S. Pat. No. 5,200,562 discloses a key position computing apparatus and method therefor which includes optical sensing devices for each key to detect key movement. Information from the sensing devices is processed to determine key positions.
U.S. Pat. No. 5,237,125 discloses a method and apparatus for measuring velocity of key motion in a keyboard operated musical instrument wherein sensors having a polymeric piezoelectric film are mounted proximate to keys on a keyboard. Upon deflection of the keys, the sensors produce an output which is digitized and processed to create musical information according to detected key velocities.
As can be seen therefore, a variety of devices, methods, and systems for sensing and recording key movement in keyboard instruments have been developed. The above devices, methods and systems, however, rely on sensing the position and velocity of the keys themselves. Typically, sensors in prior systems are positioned above the keys and point downward, or beneath the keys pointing upward, so as to detect the amount of light reflected back from the keys. Note duration is generally calculated by determining the difference in time from when the key is started to be pressed by the performer and when the key is fully depressed, whereas velocity is determined from the relationship of the distance and time of travel.
A number of deficiencies have become apparent in the aforementioned methods and devices, however. Musical expression information is difficult to sense and record accurately based on the velocity and position of the keys themselves, since key movement may not accurately reflect the musical notes ultimately produced. A particular problem experienced is that musical expression information is especially difficult to sense and record accurately in keyboard instruments in which the keys actuate hammers which strike strings, such as the piano. For example, pianos typically vary in key weight and hammer action from manufacturer to manufacturer. The key distance between the resting position and played position also varies between manufacturers and between different piano designs. A standardized sensing and recording system capable of accurate key expression detection thus cannot be applied to every piano. In order to achieve accurate sensing and recording of key expression, the controlling software for the sensing and recording system must be modified and rewritten for each type of piano, to take into account the variation in the weight, action, and distance traveled by the keys.
Further, certain performance techniques for the piano, such as trills, involve rapid key movement, and generate musical expression which is difficult to measure by key movement. For example, the key movement may be very slight, yet the corresponding hammer action may be substantial, depending upon the individual performer. Thus, accurate musical expression information is difficult or impossible to obtain by sensing key motion.
An additional problem associated with the prior methods and devices is that sensing key motion generally involves sacrificing a portion of the key area to accommodate the sensors. This results in reduced area for performers to work with, and generally detracts from the aesthetics of the piano itself. Further, the difference in reflectivity between the black keys and white keys of a piano must be taken into account and corrected when optical sensing is used. Sensing devices and systems which measure key velocity from the interior of the piano can avoid these problems, but are difficult and time consuming to install, and can require modification of the piano itself.
Yet another drawback of prior methods and devices is that the sensors tend to generate an "on" and "off" type of output from reading key movement, resulting in omission of a great deal of musical expression information.
Regardless of the design or manufacture of a particular piano, however, measurement of the velocity and position of the hammer or hammer shank results in the same degree of accuracy in sensing musical expression. By monitoring the hammer shanks or hammers, the same sensing apparatus and method can be used on each piano without modification, to obtain a high degree of accuracy in sensing and recording of musical information.
Therefore, there is a need for an apparatus and method for sensing and recording musical expression generated by keyboard instruments which accurately records musical expression generated by keyboard instruments such as the piano, which detects motion of the hammer shanks and does not rely on the detection of key motion, which does not require software modification for different designs and manufactures of piano, which is quick and easy to install, which does not sacrifice keyboard space, and which does not detract from the aesthetic appearance of the piano. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, the applicant's claimed invention.